This invention relates to an image transmitting system and an image transmitting method for transmitting image information over a transmission line such as a LAN (local area network) line or a public line. Further, the present invention also relates to color facsimile machines, or to transmission/reception of images of the Internet.
To transmit a color image, JPEG coding is often used if the original is a picture, a photo, etc. In the JPEG coding, first, an input image is divided into blocks, then orthogonal transformation is performed for each block. Quantization processing is performed for the resultant orthogonal transformation output and the provided quantization output is coded, compressed, and transmitted. However, the following problem is pointed out for the technique: If the technique is applied to text or a line drawing, degradation of mosquito noise, etc., is easily produced.
As a method for solving this problem, the Unexamined Japanese Patent Application Publication No. Hei 6-292018 proposes a method wherein an orthogonal transformation coding system is provided with new text block detection means and the quantization width for a block containing a large quantity of edge components, such as a text block, is made finer than that for any other block such as a picture or photo portion, thereby minimizing a quantization error of the block containing text and improving the image quality of text and line drawings.
To transmit a color multivalued image, data compression processing can be performed using a technique of orthogonal transformation, etc., as described above. However, generally, transmitted images often include monochrome document images only with black characters as well as color multivalued images. Compressing such monochrome images using a technique of orthogonal transformation, etc., like color multivalued images leads to an increase in the data amount and results in a rise in communication costs.
In recent years, an image output system that can output higher-definition color text and line drawing (multivalued) images has been developed. Accordingly, the data amount of transferred image information is larger than ever. On the other hand, considering the visual characteristics of human beings, higher resolution is a desirable trend for images with edge portions to be represented finely such as text and line drawings. However, if an image attaching importance to gradation reproducibility such as a picture or a photo is put into high resolution, an increase in the time required for image processing, the memory capacity, etc., is noticeable as compared with image reproducibility; a problem may be caused.
With conventional transmitting systems, as the image data resolution is raised to improve the text reproduction quality, the resolution of a picture or photo portion mixed in text or a line drawing is also raised; resultantly, the whole data amount becomes enormous, resulting in a rise in system and communication costs.
It is therefore an object of the invention to provide an image transmitting system and an image transmitting method which make it possible to transmit even a color image with a mixture of a picture, photo image and a text, line drawing image without degrading the image quality and with high efficiency and also are capable of transmitting monochrome images with high efficiency as before.
In the invention, whether or not input image information is a color or monochrome image or specification as to whether image information is a color or monochrome image is accepted from the user and if the image information is determined a color image or a color image is specified, the image information is transmitted in the multilayer data format consisting of a first piece of image data, a second piece of image data, and selection data for selecting either the first piece or the second piece of image data. Thus, for a color image, a picture portion, such as a photo, and a text, line drawing portion different in attribute can be processed and transmitted as different data layers, so that they can be transmitted with their respective optimum image quality and can also be compressed to their respective optimum data amounts for transmission with high efficiency.
To transmit the image information in the multilayer data format, the image information is transmitted in any one of a transmission format of transmitting only the selection data, a transmission format of transmitting the first piece of image data and the selection data, a transmission format of transmitting the second image data and the selection data, and a transmission format of transmitting the first piece of image data, the second piece of image data, and the selection data, for example, in response to the image attribute, whereby the data amount can be reduced in response to the image to be transmitted and the image can be transmitted with high efficiency.
If the input image information is determined a monochrome image or a monochrome image is specified, it is transmitted in the transmission format of transmitting only the selection data or transmission in the multilayer data format is inhibited and the image information is transmitted, for example, in the 1-layer data format consisting only of one data plane, whereby the transmission data amount of monochrome images can be drastically decreased as compared with that of color images and highly efficient transmission is enabled as before.